Category Archives: Linux

Apparently, there has been a severe security breach at Fedora. They had to rebuild their repositories and change their signing keys, and it might just be they have only rebuilt repositories for Fedora 8 and 9. Which might just explain why I have been unable to use yum to install software on a Fedora Core 5 box for several weeks now! And, yes, people, I know FC5 is no longer officially supported, but the mirrors were there and I was still using them not long ago. So, attention Fedora users! If you are using a Fedora release below 8, you should probably consider re-installing a recent release or risk staying stuck with a system with no software updates and no packages.

Tsung has a “proxy mode” which records SQL statements and produces an appropriate Tsung scenario file. What could be simpler? I shall just point my web application to speak to the Tsung proxy instead of the database and I will use it to generate “typical usage” cases.

Unfortunately, this is not an option if, say, your application uses a web framework which maintains several open connections to the database server. The Tsung proxy can only handle one connection at a time. So your application does not function properly and you are not able to use it to generate the “typical usage” scenaria.

Then there is pgFouine, a PostgreSQL log analyzer, which shows some promise, which produces Tsung compatible output on demand. But pgFouine principally analyzes log files to group and rank statements according to how well they perform in the database, and this approach has spilled over to Tsung scenario file generation: the order of the SQL statements is not preserved! This, by itself, perhaps would not be a problem, but I often record multiple use-cases in one go and pgFouine mixes them up.

The best way to create our test cases, therefore, is to use the log files from an idle Postgresql server, after enabling the logging of all SQL statements in the server. I have written a few scripts which help with the process, but this was after already changing the logging format of our Postgresql server to pgFouine’s requirements (syslog). Thus, the Postgresql server needs to log in this particular style:

For the changes to have effect, you need to restart the syslog service (/etd/init.d/syslog restart) and Postgresql.

You are now ready to start capturing SQL statements in the Postgresql log file. To make sure you shall be able to filter the log file into separate use-cases, you should choose a unique string identifier (e.g. ‘complex search 001’) to throw at the database server at the beginning and end of a particular use-case. You may do this by connecting to the server via ssh and typing:

echo "SELECT 'complex search 001';" | psql -U postgres

… before using your web application (which must be configured to talk to this particular Postgresql server). At the end of this use-case (‘complex search 001’) all you need to do is repeat the line above.

When you have finished recording all batches (use-cases) of SQL statements, you need to locate the postgresql log file (e.g. /var/log/postgresql/postgresql.log) and use it as input for the perl script below:

I have created syslog-filter, a simple perl script you may run from the command line, like so:

… assuming the script has permission to be executed and is located in the same directory as the postgresql.log file. This command creates complex-search-001.log, which contains only those SQL statement that belong to this use-case.

This generates a partial Tsung file in the proper format. This process need to be repeated for every different use-case we would like to include. The resulting xml files may be concatenated into a single file, like so:

cat *.xml > my-tsung-scenario.xml

The resulting file (my-tsung-scenario.xml) will be completed into a full valid Tsung scenario file in section 2.4 In order to run the above scripts, you obviously need a working Perl environment and the Parse::Syslog perl module, which may be installed by typing (as root):

cpan Parse::Syslog

Before proceeding any further, you may want to manually edit all occurences of

<transaction name="requests">

…in my-tsung-scenario.xml, changing the name each time to reflect the use-case which follows. E.g.

<transaction name="complexSearch1">

Another required manual edit concerns the probability factors assigned to each use-case (session). Therefore, you need to adjust the probability settings of all such occurences:

… to get a head-tsung-scenario.xml file which we can then edit accoring to our needs. If we keep the existing settings, Tsung will attempt to load-test a server called myserver (the names needs to be resolvable, please check your DNS service and/or your /etc/hosts file) from a single client, myclient, while trying to monitor hardware load on both machines. In the load section, two load phases have been defined, starting at “new user every 4 seconds” and then doubling the rate. Each of these phases is meant to last half an hour (1800s), but once the server reaches its breaking point, user sessions do not terminate properly and the duration of the load phase we are in is expanded, as Tsung waits for all users to finish before proceeding to the next one. Once you have changed head-tsung-scenario.xml according to your needs, you may complete the generation of a new scenario file by typing:

This file (temp-tsung-scenario.xml) is actually a full valid scenario file which may be used for testing. But you probably want to tweak one or two things to make this testing relevant to your system, which is what we shall discuss in the next installment of this tutorial.

If you suddenly needed a cronnable Postgresql database update command for SQL text files, you would probably just type:

cat /path/to/some/dir/*.sql | psql -U postgres someDatabase

So, I am asking myself, have I created something pointless?

As it turns out:

pgBee keeps track of the update process. If a pgBee instance is killed, the next invocation will carry on from where the previous one has stopped. And if it finds SQL errors, it will report how far it got in the input files before quitting.

pgBee is actually faster than psql when executing SQL statements from a text file. psql took 112m (with one transaction for each statement), psql -1 took 97m (with one transaction for the entire file) but pgBee finished in 21m !!! (with one transaction per batch) That’s a whopping 898 operations per second. All tests were run on the same database server (localhost), pgBee was batching groups of 100 statements at a time and a real data file was used, with 1131753 SQL statements in total (511335 DELETEs and 567577 INSERTs).

pgBee is a set of Java classes I wrote for automating bulk updates of Postgresql databases on Linux servers. It requires Java (doh!) and Ant (as a build/execute front-end), it is cronnable and performs very well, especially in multi-threaded mode, which takes full advantage of multi-core CPUs in modern servers. The source of inspiration for pgBee has been previously described.

All configuration is done in the settings.xml file, but some options may be set through the command line, e.g.

ant -f /path/to/build.xml -Dlock=yes -Dthreads=8 -Dparallel=yes run

pgBee processes all files it finds in a particular (in) directory and moves them to either a done directory or a rejects directory, if there were SQL errors. You’ll need to create the right directory structure and configure pgBee settings before starting. The pgBee process catches SIGTERM, SIGHUP etc. signals and exits gracefully, ready to resume from where it stopped the next time it is run. So, it should be quite reliable, in the absence of hard resets and kill -9. Having said that, I am supplying no guarantees of fitness for any purpose of any kind 🙂 Please use at your own risk.

If you need to make sure a particular set of statements is processed in the same transaction, you only have to include all statements in the same line of an input file, separated by semi-colons. There’s no limit to how many SQL statements you may include in a single line. More information about input file format, usage and configuration may be found in the downloadable tarball

My new work computer is a Dell Vostro 1310 laptop. I am most chuffed with this new machine, as this is my first modern, up-to-date programming notebook for a long time now (some people think it’s boxy! but all I want is a no-nonsense machine). And it runs Debian Lenny, which marks a change from my old Ubuntu and Slackware days. So, this is me showing off a new laptop and sharing some issues for anyone wanting to install Debian Linux on a Vostro 1310.

Installing Debian Lenny 64-bit (amd64)

For the record, my first attempts at installing Linux on this box were very frustrating, as both Ubuntu 8.04 and 8.10 64-bit versions wouldn’t correctly recognise the Ethernet card (Realtek 8168) – which is the last thing I’d expect not to work. Same thing happened with 64-bit Debian Sarge. I was getting frustrated by the time I tried 64-bit Debian Lenny, but things suddenly worked out of the box and installation was a breeze (using the netinst CD).

I decided to go for the easy option and install Windows drivers for the WiFi card through ndiswrapper. The process is relatively straightforward:

You should now have a wlan0 interface to configure for WiFi connections (you might want also want to install wifi-radar). The rmmod ssb etc. stuff needs to happen every time the system boots. I have written a simple initialization script that does this.

Now, I thought I was having a Bluetooth problem, until I noticed I had switched off WiFi and Bluetooth using the little switch at the right side of the laptop, next to the DVD drive slot. As it happens, Bluetooth worked out of the box, but please have a look at this if you have Vista pre-installed: http://onemansjourneyintolinux.blogspot.com/2007/10/enabling-bluetooth.html

I had opted for Windows XP pre-installed with Vista installation media, so I didn’t experience any problems. In fact, I routinely use Bluetooth to connect to my 3skypephone mobile and use it as a 3G modem. Please have a look at this, if you are interested.

I have also installed NVIDIA drivers for the video card (here’s one of many tutorials) and Compiz-Fusion, which looks quite nice! Here’s a brief video:

Screen capture (with recordmydesktop) was a bit flickery, sorry, but I was stressing the machine: I was using loads of Compiz-Fusion eye-candy and installing Vista as a virtual machine through VirtualBox at the same time.

Suspend and Hibernate work out-of-the-box. All-in-all, this laptop gives me everything I need for heavy development work – power management, connectivity, performance (and eye candy to impress co-workers). I don’t know if the fingerprint scanner works, I haven’t even thought about using it yet.

My only real complaint up to now is audio 😦 This is an interesting story, actually, because I had sound when I first installed Lenny about a month ago (well, without headphone jack sense) and then I went for a kernel update, which broke sound! The sound device now doesn’t even show up in the operating system, so it’s no use recompiling ALSA (which I have done, just in case). Now, Lenny has not been officially branded as a “stable” release yet, this is supposed to happen in 1-2 months, so here’s hoping one of these days I do a system update and suddenly everything works (again). But, as I said earlier, I am using this laptop as a development box, so lack of sound doesn’t really affect me. It’d be nice, however, to be able to listen to some mp3s while at work, which I do through my n800 (as a quick fix).

Update (2008-11-21): A prerelease version of Adobe Flash player 10 has just been released for Linux 64-bit systems. You may find it here. I installed it by extracting and copying libflashplayer.so to /usr/local/lib and updating the /etc/alternatives/flash-mozilla.so symbolic link to point to /usr/local/lib/libflashplayer.so

Update (2009-02-09): The real problem with sound on this laptop is that the operating system does not even recognise there is a soundcard in the system (there is no audio controller in the lspci output). A few days ago, I decided to update my kernel to 2.6.26-1-amd64 using apt-get, just in case it would make a difference. Well, it doesn’t 😦 I have downloaded my kernel’s headers and recompiled the latest version of ALSA (1.0.19), but the audio controller just doesn’t show up. So, I’ve bought myself a cheap (10 EUR) C-Media based USBsound card, which works fine (mic too).

Have you ever wondered how and why things are organised in Linux filesystems? Do /opt, /var, /home, /usr baffle and confuse you? Now, I have been a Linux user for several years and, having used several different Linux distributions I have a pretty good idea where things usually reside. But, somehow, I hadn’t come across this before, and it’s such a useful thing to have read, especially if you are a linux newbie! Thanks, Lance.